353 people were killed and 1669 were seriously injured while by open motorboats. Personal watercraft (i.e., jetskis) had the second highest casualty rate with 45 deaths and 920 injuries. The top two causes of death in these motorboat accidents were drowning and trauma, which combined for nearly 90% of all deaths. To learn more, check out this article written by my colleague.
Common Causes of Motorboat Accidents and Drownings